1. Field of the Invention
This invention relates to a zoom lens, and more particularly to a zoom lens for a video camera using a solid-state image pickup device.
2. Description of the Related Art
A conventional focusing method for a zoom lens is a so-called inner focusing method which has contributed to miniaturizing a zoom lens system and minimizing a focusing distance. For example, Japanese Laid-Open Patent Application Publication No. Sho 59-30515 discloses a method of moving a part of a zoom lens group only when the zoom lens is focused. Japanese Laid-Open Patent Application Publication No. Hei 2-48620 discloses a method of moving a zoom lens group which is arranged in the rear of the zoom lens system and serves as a compensator.
However, the above-mentioned types of zoom lenses encounter the following problems: (1) miniaturizing a zoom lens system has not been successful, and (2) the quality of an image at a short photographic range has not been improved.